1. Field of the Invention
The present invention relates to image recording apparatuses, and more particularly to a liquid-discharge-head recovering device.
2. Description of the Related Art
Liquid discharge heads, such as inkjet print heads, are widely used in, for example, inkjet printers and have been researched for many years. There are problems existing in conventional liquid discharge heads in that the nozzles disposed in the discharging surface cannot properly discharge liquid or that the discharging direction of the liquid may deviate from the intended direction. This can be caused when the liquid (for example, an ink solvent) in the nozzles evaporates, increasing the viscosity of the liquid in each nozzle, or when foreign matter, such as paper dust, becomes attached to the nozzles.
For these reasons, inkjet printers are generally provided with a liquid-discharge-head recovering device which includes, for example, a liquid-discharge-head cap for preventing the evaporation of the liquid (ink solvent) in the nozzles; a suction unit for sucking out and removing the thickened liquid (ink) from the nozzles; and a wiping unit for wiping off the liquid remaining on the discharging surface and any foreign matter, such as paper dust, attached to the discharging surface.
FIG. 10 is a schematic plan view of a conventional liquid-discharge-head cap 410. FIG. 11 is a cross-sectional view of a discharge head 300 and the cap 410 taken along line XI—XI in FIG. 10. Specifically, the plan view of FIG. 10 is viewed from a direction indicated by an arrow V shown in FIG. 11. Referring to FIGS. 10 and 11, the discharge head 300 is an inkjet print head having a discharging surface 301 in which nozzles are disposed. The liquid-discharge-head cap 410 is generally formed of an elastic material, such as rubber, so that the contact between the cap 410 and the discharging surface 301 can be properly maintained. Moreover, the cap 410 has a base 411.
The cap 410 is driven by a known cap-driving unit, such as a cam or a motor, and is movable in directions indicated by an arrow G in FIG. 11. Specifically, the cap 410 is capable of moving back and forth to come into and out of contact with the discharging surface 301, that is, between a capping position and a non-contact position, which is not shown in FIG. 11.
The base 411 of the cap 410 is provided with a suction opening 412, and this suction opening 412 is connected with a suction tube 420. Moreover, the suction tube 420 is connected with a suction pump 425 which functions as a pressure-reducing source. When the cap 410 is in the capping position, the suction pump 425 performs a suction process via the suction opening 412 to reduce the pressure in a space 450 formed between the cap 410 and the discharging surface 301.
Furthermore, the base 411 is provided with an air-communication opening 413, and this air-communication opening 413 is connected with an air-communication tube 430. Moreover, the air-communication tube 430 is connected with an air-communication valve 435 which functions as an air-communication controlling element. The valve 435 is for controlling whether to open or close the communication between the space 450 and the atmosphere via the air-communication opening 413. As shown in FIGS. 10 and 11, the space 450 of the cap 410 includes an absorber 440 formed of an ink-absorptive porous material.
A suction process of a typical liquid-discharge-head recovering device provided with the liquid-discharge-head cap 410 described above will now be described.
For performing the suction process, the cap 410 is first set at the non-contact position, and the discharge head 300 is moved to a position where it faces the cap 410. The cap 410 is then moved to a capping position by means of the cap-driving unit. Subsequently, the air-communication valve 435 is closed. The suction pump 425 then operates so as to reduce the pressure in the space 450.
Consequently, the ink is sucked out from the nozzles of the discharge head 300. The ink removed from the nozzles is absorbed by the ink absorber 440, but is immediately drawn into the suction pump 425. Subsequently, the air-communication valve 435 opens and connects the space 450 with the atmosphere. In most recovering devices, the suction pump 425 remains in an operative state after the air-communication valve 435 is opened so that the ink remaining in the space 450, especially the ink absorbed in the ink absorber 440, can be drawn into the suction pump 425. The cap 410 is then driven to the non-contact position, i.e. an unsealing position, by means of the cap-driving unit. The suction pump 425 is drained by an ink drainage process such that the ink drawn into the suction pump 425 is emitted out of the recovering device in a direction indicated by an arrow W in FIG. 11.
In most cases, after performing such a suction process, some of the ink sucked out from the nozzles remains on the discharging surface 301. This may be problematic if the ink remaining on the discharging surface 301 covers the nozzles since it may lead to improper discharging of liquid or deviation of the discharging direction of liquid, as described previously. To prevent such problems, most inkjet printers are provided with a wiping unit for wiping off the ink remaining on the discharging surface 301 after the suction process. This effectively prevents the problems described above, such as the improper discharging of liquid and the deviation of the discharging direction of liquid.
In recent years, small-sized inkjet printers have been widely manufactured. Such small-size inkjet printers are mainly used for printing images taken by, for example, digital cameras, on relatively small-size paper, such as A6-size paper. For reducing the size of such printers, the ink capacity of the printer must be relatively reduced as much as possible. For this reason, the amount of ink to be sucked out from the nozzles during the suction process must also be reduced to the greatest extent possible.
To fulfill such demands, a negative-pressure valve may be disposed in a section of the suction tube 420 between the suction opening 412 and the suction pump 425. This negative-pressure valve is an on-off valve that allows the pressure in the space 450 to be reduced by means of the suction pump 425. In detail, in a state where the negative-pressure valve is closed, the suction pump 425 begins its operation so as to reduce the pressure in a space in the suction tube 420 between the negative-pressure valve and the suction pump 425. Thus, the pressure in this space in the suction tube 420 is highly reduced with respect to the ambient pressure. This highly-reduced pressure will be referred to as high negative pressure hereinafter. Subsequently, when the high negative pressure reaches a predetermined value and the negative-pressure valve opens, the pressure in the space 450 in the cap 410 is reduced at once. Shortly after the negative-pressure valve is opened, the air-communication valve 435 is opened. This suction process, which utilizes high negative pressure, is effective due to the fact that the pressure in the space 450 is greatly reduced in an extremely short period of time. Specifically, this reduces the amount of ink sucked out from the nozzles, and moreover, effectively removes, for example, thickened ink attached around each nozzle and bubbles formed inside the nozzles.
However, when performing the suction process using high negative pressure in the conventional liquid-discharge-head recovering devices, the amount of ink remaining on the discharging surface 301 may increase due to the following reasons. Because the air-communication valve 435 opens shortly after the negative-pressure valve is opened, an extremely high negative pressure still remains in the space 450 just before the air-communication valve 435 is opened. For this reason, when the air-communication valve 435 opens, atmospheric gas enters the space 450 at an extremely high rate through the air-communication opening 413. The ink present in the space 450 when the air-communication valve 435 is opened, that is, the ink previously sucked out from the nozzles when the negative-pressure valve opened, spatters in various directions in the space 450 due to the fast-flowing gas.
In a case where a large amount of ink is present in the vicinity of the air-communication opening 413, the amount of ink spattering is relatively large and may even reach the contact section between the discharging surface 301 and the cap 410. Thus, even if the suction pump 425 continues to operate in this state, the suction pump 425 may be able to suck in the ink absorbed in the ink absorber 440 but not the ink present in other regions within the space 450 of the cap 410. For this reason, the ink attached to the discharging surface 301 may remain even after the cap 410 is moved to the non-contact position. Of all the ink remaining in the contact section between the discharging surface 301 and the cap 410, the amount of ink remaining in the contact section near the air-communication opening 413 is especially large.
Accordingly, for performing the suction process using high negative pressure in the conventional recovering devices, the amount of ink remaining on the discharging surface 301 is large in comparison with performing the suction process without using the high negative pressure. The larger amount of ink left on the discharging surface 301 may be problematic for the subsequent wiping process, which is generally performed after the suction process, in that the ink may spatter to various parts of the inkjet printer during the wiping process, and moreover, that the ink may attach to, for example, a wiper blade used for the wiping process and may thicken when the wiper blade is left unused.